  Wolfenite.  
I'm not sure why I have this mineral: I think it may have been a free sample included with some other mineral purchase.  In any case, it's quite lovely, and unusual in chemical composition: Lead and molybdenum. 
Source: eBay 
Contributor: Theodore Gray 
Acquired: 15 October, 2005 
Price: Donated 
Size: 0.25" 
Composition: Pb(MoO4)
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